Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

3 files changed, 889 insertions, 0 deletions

diff --git a/arch/um/os-Linux/skas/Makefile b/arch/um/os-Linux/skas/Makefile
new file mode 100644
index 000000000..c4566e788
--- /dev/null
+++ b/arch/um/os-Linux/skas/Makefile
@@ -0,0 +1,10 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2002 - 2007 Jeff Dike (jdike@{linux.intel,addtoit}.com)
+#
+
+obj-y := mem.o process.o
+
+USER_OBJS := $(obj-y)
+
+include arch/um/scripts/Makefile.rules
diff --git a/arch/um/os-Linux/skas/mem.c b/arch/um/os-Linux/skas/mem.c
new file mode 100644
index 000000000..c546d16f8
--- /dev/null
+++ b/arch/um/os-Linux/skas/mem.c
@@ -0,0 +1,207 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stddef.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <init.h>
+#include <as-layout.h>
+#include <mm_id.h>
+#include <os.h>
+#include <ptrace_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <sysdep/ptrace.h>
+#include <sysdep/stub.h>
+
+extern char batch_syscall_stub[], __syscall_stub_start[];
+
+extern void wait_stub_done(int pid);
+
+static inline unsigned long *check_init_stack(struct mm_id * mm_idp,
+					      unsigned long *stack)
+{
+	if (stack == NULL) {
+		stack = (unsigned long *) mm_idp->stack + 2;
+		*stack = 0;
+	}
+	return stack;
+}
+
+static unsigned long syscall_regs[MAX_REG_NR];
+
+static int __init init_syscall_regs(void)
+{
+	get_safe_registers(syscall_regs, NULL);
+	syscall_regs[REGS_IP_INDEX] = STUB_CODE +
+		((unsigned long) batch_syscall_stub -
+		 (unsigned long) __syscall_stub_start);
+	return 0;
+}
+
+__initcall(init_syscall_regs);
+
+static inline long do_syscall_stub(struct mm_id * mm_idp, void **addr)
+{
+	int n, i;
+	long ret, offset;
+	unsigned long * data;
+	unsigned long * syscall;
+	int err, pid = mm_idp->u.pid;
+
+	n = ptrace_setregs(pid, syscall_regs);
+	if (n < 0) {
+		printk(UM_KERN_ERR "Registers - \n");
+		for (i = 0; i < MAX_REG_NR; i++)
+			printk(UM_KERN_ERR "\t%d\t0x%lx\n", i, syscall_regs[i]);
+		panic("do_syscall_stub : PTRACE_SETREGS failed, errno = %d\n",
+		      -n);
+	}
+
+	err = ptrace(PTRACE_CONT, pid, 0, 0);
+	if (err)
+		panic("Failed to continue stub, pid = %d, errno = %d\n", pid,
+		      errno);
+
+	wait_stub_done(pid);
+
+	/*
+	 * When the stub stops, we find the following values on the
+	 * beginning of the stack:
+	 * (long )return_value
+	 * (long )offset to failed sycall-data (0, if no error)
+	 */
+	ret = *((unsigned long *) mm_idp->stack);
+	offset = *((unsigned long *) mm_idp->stack + 1);
+	if (offset) {
+		data = (unsigned long *)(mm_idp->stack + offset - STUB_DATA);
+		printk(UM_KERN_ERR "do_syscall_stub : ret = %ld, offset = %ld, "
+		       "data = %p\n", ret, offset, data);
+		syscall = (unsigned long *)((unsigned long)data + data[0]);
+		printk(UM_KERN_ERR "do_syscall_stub: syscall %ld failed, "
+		       "return value = 0x%lx, expected return value = 0x%lx\n",
+		       syscall[0], ret, syscall[7]);
+		printk(UM_KERN_ERR "    syscall parameters: "
+		       "0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx\n",
+		       syscall[1], syscall[2], syscall[3],
+		       syscall[4], syscall[5], syscall[6]);
+		for (n = 1; n < data[0]/sizeof(long); n++) {
+			if (n == 1)
+				printk(UM_KERN_ERR "    additional syscall "
+				       "data:");
+			if (n % 4 == 1)
+				printk("\n" UM_KERN_ERR "      ");
+			printk("  0x%lx", data[n]);
+		}
+		if (n > 1)
+			printk("\n");
+	}
+	else ret = 0;
+
+	*addr = check_init_stack(mm_idp, NULL);
+
+	return ret;
+}
+
+long run_syscall_stub(struct mm_id * mm_idp, int syscall,
+		      unsigned long *args, long expected, void **addr,
+		      int done)
+{
+	unsigned long *stack = check_init_stack(mm_idp, *addr);
+
+	*stack += sizeof(long);
+	stack += *stack / sizeof(long);
+
+	*stack++ = syscall;
+	*stack++ = args[0];
+	*stack++ = args[1];
+	*stack++ = args[2];
+	*stack++ = args[3];
+	*stack++ = args[4];
+	*stack++ = args[5];
+	*stack++ = expected;
+	*stack = 0;
+
+	if (!done && ((((unsigned long) stack) & ~UM_KERN_PAGE_MASK) <
+		     UM_KERN_PAGE_SIZE - 10 * sizeof(long))) {
+		*addr = stack;
+		return 0;
+	}
+
+	return do_syscall_stub(mm_idp, addr);
+}
+
+long syscall_stub_data(struct mm_id * mm_idp,
+		       unsigned long *data, int data_count,
+		       void **addr, void **stub_addr)
+{
+	unsigned long *stack;
+	int ret = 0;
+
+	/*
+	 * If *addr still is uninitialized, it *must* contain NULL.
+	 * Thus in this case do_syscall_stub correctly won't be called.
+	 */
+	if ((((unsigned long) *addr) & ~UM_KERN_PAGE_MASK) >=
+	   UM_KERN_PAGE_SIZE - (10 + data_count) * sizeof(long)) {
+		ret = do_syscall_stub(mm_idp, addr);
+		/* in case of error, don't overwrite data on stack */
+		if (ret)
+			return ret;
+	}
+
+	stack = check_init_stack(mm_idp, *addr);
+	*addr = stack;
+
+	*stack = data_count * sizeof(long);
+
+	memcpy(stack + 1, data, data_count * sizeof(long));
+
+	*stub_addr = (void *)(((unsigned long)(stack + 1) &
+			       ~UM_KERN_PAGE_MASK) + STUB_DATA);
+
+	return 0;
+}
+
+int map(struct mm_id * mm_idp, unsigned long virt, unsigned long len, int prot,
+	int phys_fd, unsigned long long offset, int done, void **data)
+{
+	int ret;
+	unsigned long args[] = { virt, len, prot,
+				 MAP_SHARED | MAP_FIXED, phys_fd,
+				 MMAP_OFFSET(offset) };
+
+	ret = run_syscall_stub(mm_idp, STUB_MMAP_NR, args, virt,
+			       data, done);
+
+	return ret;
+}
+
+int unmap(struct mm_id * mm_idp, unsigned long addr, unsigned long len,
+	  int done, void **data)
+{
+	int ret;
+	unsigned long args[] = { (unsigned long) addr, len, 0, 0, 0,
+				 0 };
+
+	ret = run_syscall_stub(mm_idp, __NR_munmap, args, 0,
+			       data, done);
+
+	return ret;
+}
+
+int protect(struct mm_id * mm_idp, unsigned long addr, unsigned long len,
+	    unsigned int prot, int done, void **data)
+{
+	int ret;
+	unsigned long args[] = { addr, len, prot, 0, 0, 0 };
+
+	ret = run_syscall_stub(mm_idp, __NR_mprotect, args, 0,
+			       data, done);
+
+	return ret;
+}
diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
new file mode 100644
index 000000000..eecde73b2
--- /dev/null
+++ b/arch/um/os-Linux/skas/process.c
@@ -0,0 +1,672 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
+ * Copyright (C) 2002- 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
+ */
+
+#include <stdlib.h>
+#include <stdbool.h>
+#include <unistd.h>
+#include <sched.h>
+#include <errno.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+#include <asm/unistd.h>
+#include <as-layout.h>
+#include <init.h>
+#include <kern_util.h>
+#include <mem.h>
+#include <os.h>
+#include <ptrace_user.h>
+#include <registers.h>
+#include <skas.h>
+#include <sysdep/stub.h>
+#include <linux/threads.h>
+
+int is_skas_winch(int pid, int fd, void *data)
+{
+	return pid == getpgrp();
+}
+
+static int ptrace_dump_regs(int pid)
+{
+	unsigned long regs[MAX_REG_NR];
+	int i;
+
+	if (ptrace(PTRACE_GETREGS, pid, 0, regs) < 0)
+		return -errno;
+
+	printk(UM_KERN_ERR "Stub registers -\n");
+	for (i = 0; i < ARRAY_SIZE(regs); i++)
+		printk(UM_KERN_ERR "\t%d - %lx\n", i, regs[i]);
+
+	return 0;
+}
+
+/*
+ * Signals that are OK to receive in the stub - we'll just continue it.
+ * SIGWINCH will happen when UML is inside a detached screen.
+ */
+#define STUB_SIG_MASK ((1 << SIGALRM) | (1 << SIGWINCH))
+
+/* Signals that the stub will finish with - anything else is an error */
+#define STUB_DONE_MASK (1 << SIGTRAP)
+
+void wait_stub_done(int pid)
+{
+	int n, status, err;
+
+	while (1) {
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
+		if ((n < 0) || !WIFSTOPPED(status))
+			goto bad_wait;
+
+		if (((1 << WSTOPSIG(status)) & STUB_SIG_MASK) == 0)
+			break;
+
+		err = ptrace(PTRACE_CONT, pid, 0, 0);
+		if (err) {
+			printk(UM_KERN_ERR "wait_stub_done : continue failed, "
+			       "errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+	}
+
+	if (((1 << WSTOPSIG(status)) & STUB_DONE_MASK) != 0)
+		return;
+
+bad_wait:
+	err = ptrace_dump_regs(pid);
+	if (err)
+		printk(UM_KERN_ERR "Failed to get registers from stub, "
+		       "errno = %d\n", -err);
+	printk(UM_KERN_ERR "wait_stub_done : failed to wait for SIGTRAP, "
+	       "pid = %d, n = %d, errno = %d, status = 0x%x\n", pid, n, errno,
+	       status);
+	fatal_sigsegv();
+}
+
+extern unsigned long current_stub_stack(void);
+
+static void get_skas_faultinfo(int pid, struct faultinfo *fi, unsigned long *aux_fp_regs)
+{
+	int err;
+
+	err = get_fp_registers(pid, aux_fp_regs);
+	if (err < 0) {
+		printk(UM_KERN_ERR "save_fp_registers returned %d\n",
+		       err);
+		fatal_sigsegv();
+	}
+	err = ptrace(PTRACE_CONT, pid, 0, SIGSEGV);
+	if (err) {
+		printk(UM_KERN_ERR "Failed to continue stub, pid = %d, "
+		       "errno = %d\n", pid, errno);
+		fatal_sigsegv();
+	}
+	wait_stub_done(pid);
+
+	/*
+	 * faultinfo is prepared by the stub_segv_handler at start of
+	 * the stub stack page. We just have to copy it.
+	 */
+	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
+
+	err = put_fp_registers(pid, aux_fp_regs);
+	if (err < 0) {
+		printk(UM_KERN_ERR "put_fp_registers returned %d\n",
+		       err);
+		fatal_sigsegv();
+	}
+}
+
+static void handle_segv(int pid, struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
+{
+	get_skas_faultinfo(pid, &regs->faultinfo, aux_fp_regs);
+	segv(regs->faultinfo, 0, 1, NULL);
+}
+
+/*
+ * To use the same value of using_sysemu as the caller, ask it that value
+ * (in local_using_sysemu
+ */
+static void handle_trap(int pid, struct uml_pt_regs *regs,
+			int local_using_sysemu)
+{
+	int err, status;
+
+	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
+		fatal_sigsegv();
+
+	if (!local_using_sysemu)
+	{
+		err = ptrace(PTRACE_POKEUSER, pid, PT_SYSCALL_NR_OFFSET,
+			     __NR_getpid);
+		if (err < 0) {
+			printk(UM_KERN_ERR "handle_trap - nullifying syscall "
+			       "failed, errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		err = ptrace(PTRACE_SYSCALL, pid, 0, 0);
+		if (err < 0) {
+			printk(UM_KERN_ERR "handle_trap - continuing to end of "
+			       "syscall failed, errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
+		if ((err < 0) || !WIFSTOPPED(status) ||
+		    (WSTOPSIG(status) != SIGTRAP + 0x80)) {
+			err = ptrace_dump_regs(pid);
+			if (err)
+				printk(UM_KERN_ERR "Failed to get registers "
+				       "from process, errno = %d\n", -err);
+			printk(UM_KERN_ERR "handle_trap - failed to wait at "
+			       "end of syscall, errno = %d, status = %d\n",
+			       errno, status);
+			fatal_sigsegv();
+		}
+	}
+
+	handle_syscall(regs);
+}
+
+extern char __syscall_stub_start[];
+
+/**
+ * userspace_tramp() - userspace trampoline
+ * @stack:	pointer to the new userspace stack page, can be NULL, if? FIXME:
+ *
+ * The userspace trampoline is used to setup a new userspace process in start_userspace() after it was clone()'ed.
+ * This function will run on a temporary stack page.
+ * It ptrace()'es itself, then
+ * Two pages are mapped into the userspace address space:
+ * - STUB_CODE (with EXEC), which contains the skas stub code
+ * - STUB_DATA (with R/W), which contains a data page that is used to transfer certain data between the UML userspace process and the UML kernel.
+ * Also for the userspace process a SIGSEGV handler is installed to catch pagefaults in the userspace process.
+ * And last the process stops itself to give control to the UML kernel for this userspace process.
+ *
+ * Return: Always zero, otherwise the current userspace process is ended with non null exit() call
+ */
+static int userspace_tramp(void *stack)
+{
+	void *addr;
+	int fd;
+	unsigned long long offset;
+
+	ptrace(PTRACE_TRACEME, 0, 0, 0);
+
+	signal(SIGTERM, SIG_DFL);
+	signal(SIGWINCH, SIG_IGN);
+
+	/*
+	 * This has a pte, but it can't be mapped in with the usual
+	 * tlb_flush mechanism because this is part of that mechanism
+	 */
+	fd = phys_mapping(to_phys(__syscall_stub_start), &offset);
+	addr = mmap64((void *) STUB_CODE, UM_KERN_PAGE_SIZE,
+		      PROT_EXEC, MAP_FIXED | MAP_PRIVATE, fd, offset);
+	if (addr == MAP_FAILED) {
+		printk(UM_KERN_ERR "mapping mmap stub at 0x%lx failed, "
+		       "errno = %d\n", STUB_CODE, errno);
+		exit(1);
+	}
+
+	if (stack != NULL) {
+		fd = phys_mapping(to_phys(stack), &offset);
+		addr = mmap((void *) STUB_DATA,
+			    UM_KERN_PAGE_SIZE, PROT_READ | PROT_WRITE,
+			    MAP_FIXED | MAP_SHARED, fd, offset);
+		if (addr == MAP_FAILED) {
+			printk(UM_KERN_ERR "mapping segfault stack "
+			       "at 0x%lx failed, errno = %d\n",
+			       STUB_DATA, errno);
+			exit(1);
+		}
+	}
+	if (stack != NULL) {
+		struct sigaction sa;
+
+		unsigned long v = STUB_CODE +
+				  (unsigned long) stub_segv_handler -
+				  (unsigned long) __syscall_stub_start;
+
+		set_sigstack((void *) STUB_DATA, UM_KERN_PAGE_SIZE);
+		sigemptyset(&sa.sa_mask);
+		sa.sa_flags = SA_ONSTACK | SA_NODEFER | SA_SIGINFO;
+		sa.sa_sigaction = (void *) v;
+		sa.sa_restorer = NULL;
+		if (sigaction(SIGSEGV, &sa, NULL) < 0) {
+			printk(UM_KERN_ERR "userspace_tramp - setting SIGSEGV "
+			       "handler failed - errno = %d\n", errno);
+			exit(1);
+		}
+	}
+
+	kill(os_getpid(), SIGSTOP);
+	return 0;
+}
+
+int userspace_pid[NR_CPUS];
+int kill_userspace_mm[NR_CPUS];
+
+/**
+ * start_userspace() - prepare a new userspace process
+ * @stub_stack:	pointer to the stub stack. Can be NULL, if? FIXME:
+ *
+ * Setups a new temporary stack page that is used while userspace_tramp() runs
+ * Clones the kernel process into a new userspace process, with FDs only.
+ *
+ * Return: When positive: the process id of the new userspace process,
+ *         when negative: an error number.
+ * FIXME: can PIDs become negative?!
+ */
+int start_userspace(unsigned long stub_stack)
+{
+	void *stack;
+	unsigned long sp;
+	int pid, status, n, flags, err;
+
+	/* setup a temporary stack page */
+	stack = mmap(NULL, UM_KERN_PAGE_SIZE,
+		     PROT_READ | PROT_WRITE | PROT_EXEC,
+		     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+	if (stack == MAP_FAILED) {
+		err = -errno;
+		printk(UM_KERN_ERR "start_userspace : mmap failed, "
+		       "errno = %d\n", errno);
+		return err;
+	}
+
+	/* set stack pointer to the end of the stack page, so it can grow downwards */
+	sp = (unsigned long) stack + UM_KERN_PAGE_SIZE - sizeof(void *);
+
+	flags = CLONE_FILES | SIGCHLD;
+
+	/* clone into new userspace process */
+	pid = clone(userspace_tramp, (void *) sp, flags, (void *) stub_stack);
+	if (pid < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "start_userspace : clone failed, "
+		       "errno = %d\n", errno);
+		return err;
+	}
+
+	do {
+		CATCH_EINTR(n = waitpid(pid, &status, WUNTRACED | __WALL));
+		if (n < 0) {
+			err = -errno;
+			printk(UM_KERN_ERR "start_userspace : wait failed, "
+			       "errno = %d\n", errno);
+			goto out_kill;
+		}
+	} while (WIFSTOPPED(status) && (WSTOPSIG(status) == SIGALRM));
+
+	if (!WIFSTOPPED(status) || (WSTOPSIG(status) != SIGSTOP)) {
+		err = -EINVAL;
+		printk(UM_KERN_ERR "start_userspace : expected SIGSTOP, got "
+		       "status = %d\n", status);
+		goto out_kill;
+	}
+
+	if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
+		   (void *) PTRACE_O_TRACESYSGOOD) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "start_userspace : PTRACE_OLDSETOPTIONS "
+		       "failed, errno = %d\n", errno);
+		goto out_kill;
+	}
+
+	if (munmap(stack, UM_KERN_PAGE_SIZE) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "start_userspace : munmap failed, "
+		       "errno = %d\n", errno);
+		goto out_kill;
+	}
+
+	return pid;
+
+ out_kill:
+	os_kill_ptraced_process(pid, 1);
+	return err;
+}
+
+void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
+{
+	int err, status, op, pid = userspace_pid[0];
+	/* To prevent races if using_sysemu changes under us.*/
+	int local_using_sysemu;
+	siginfo_t si;
+
+	/* Handle any immediate reschedules or signals */
+	interrupt_end();
+
+	while (1) {
+		if (kill_userspace_mm[0])
+			fatal_sigsegv();
+
+		/*
+		 * This can legitimately fail if the process loads a
+		 * bogus value into a segment register.  It will
+		 * segfault and PTRACE_GETREGS will read that value
+		 * out of the process.  However, PTRACE_SETREGS will
+		 * fail.  In this case, there is nothing to do but
+		 * just kill the process.
+		 */
+		if (ptrace(PTRACE_SETREGS, pid, 0, regs->gp)) {
+			printk(UM_KERN_ERR "userspace - ptrace set regs "
+			       "failed, errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		if (put_fp_registers(pid, regs->fp)) {
+			printk(UM_KERN_ERR "userspace - ptrace set fp regs "
+			       "failed, errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		/* Now we set local_using_sysemu to be used for one loop */
+		local_using_sysemu = get_using_sysemu();
+
+		op = SELECT_PTRACE_OPERATION(local_using_sysemu,
+					     singlestepping(NULL));
+
+		if (ptrace(op, pid, 0, 0)) {
+			printk(UM_KERN_ERR "userspace - ptrace continue "
+			       "failed, op = %d, errno = %d\n", op, errno);
+			fatal_sigsegv();
+		}
+
+		CATCH_EINTR(err = waitpid(pid, &status, WUNTRACED | __WALL));
+		if (err < 0) {
+			printk(UM_KERN_ERR "userspace - wait failed, "
+			       "errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		regs->is_user = 1;
+		if (ptrace(PTRACE_GETREGS, pid, 0, regs->gp)) {
+			printk(UM_KERN_ERR "userspace - PTRACE_GETREGS failed, "
+			       "errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		if (get_fp_registers(pid, regs->fp)) {
+			printk(UM_KERN_ERR "userspace -  get_fp_registers failed, "
+			       "errno = %d\n", errno);
+			fatal_sigsegv();
+		}
+
+		UPT_SYSCALL_NR(regs) = -1; /* Assume: It's not a syscall */
+
+		if (WIFSTOPPED(status)) {
+			int sig = WSTOPSIG(status);
+
+			ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
+
+			switch (sig) {
+			case SIGSEGV:
+				if (PTRACE_FULL_FAULTINFO) {
+					get_skas_faultinfo(pid,
+							   &regs->faultinfo, aux_fp_regs);
+					(*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
+							     regs);
+				}
+				else handle_segv(pid, regs, aux_fp_regs);
+				break;
+			case SIGTRAP + 0x80:
+			        handle_trap(pid, regs, local_using_sysemu);
+				break;
+			case SIGTRAP:
+				relay_signal(SIGTRAP, (struct siginfo *)&si, regs);
+				break;
+			case SIGALRM:
+				break;
+			case SIGIO:
+			case SIGILL:
+			case SIGBUS:
+			case SIGFPE:
+			case SIGWINCH:
+				block_signals_trace();
+				(*sig_info[sig])(sig, (struct siginfo *)&si, regs);
+				unblock_signals_trace();
+				break;
+			default:
+				printk(UM_KERN_ERR "userspace - child stopped "
+				       "with signal %d\n", sig);
+				fatal_sigsegv();
+			}
+			pid = userspace_pid[0];
+			interrupt_end();
+
+			/* Avoid -ERESTARTSYS handling in host */
+			if (PT_SYSCALL_NR_OFFSET != PT_SYSCALL_RET_OFFSET)
+				PT_SYSCALL_NR(regs->gp) = -1;
+		}
+	}
+}
+
+static unsigned long thread_regs[MAX_REG_NR];
+static unsigned long thread_fp_regs[FP_SIZE];
+
+static int __init init_thread_regs(void)
+{
+	get_safe_registers(thread_regs, thread_fp_regs);
+	/* Set parent's instruction pointer to start of clone-stub */
+	thread_regs[REGS_IP_INDEX] = STUB_CODE +
+				(unsigned long) stub_clone_handler -
+				(unsigned long) __syscall_stub_start;
+	thread_regs[REGS_SP_INDEX] = STUB_DATA + UM_KERN_PAGE_SIZE -
+		sizeof(void *);
+#ifdef __SIGNAL_FRAMESIZE
+	thread_regs[REGS_SP_INDEX] -= __SIGNAL_FRAMESIZE;
+#endif
+	return 0;
+}
+
+__initcall(init_thread_regs);
+
+int copy_context_skas0(unsigned long new_stack, int pid)
+{
+	int err;
+	unsigned long current_stack = current_stub_stack();
+	struct stub_data *data = (struct stub_data *) current_stack;
+	struct stub_data *child_data = (struct stub_data *) new_stack;
+	unsigned long long new_offset;
+	int new_fd = phys_mapping(to_phys((void *)new_stack), &new_offset);
+
+	/*
+	 * prepare offset and fd of child's stack as argument for parent's
+	 * and child's mmap2 calls
+	 */
+	*data = ((struct stub_data) {
+			.offset	= MMAP_OFFSET(new_offset),
+			.fd     = new_fd
+	});
+
+	err = ptrace_setregs(pid, thread_regs);
+	if (err < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_SETREGS "
+		       "failed, pid = %d, errno = %d\n", pid, -err);
+		return err;
+	}
+
+	err = put_fp_registers(pid, thread_fp_regs);
+	if (err < 0) {
+		printk(UM_KERN_ERR "copy_context_skas0 : put_fp_registers "
+		       "failed, pid = %d, err = %d\n", pid, err);
+		return err;
+	}
+
+	/* set a well known return code for detection of child write failure */
+	child_data->err = 12345678;
+
+	/*
+	 * Wait, until parent has finished its work: read child's pid from
+	 * parent's stack, and check, if bad result.
+	 */
+	err = ptrace(PTRACE_CONT, pid, 0, 0);
+	if (err) {
+		err = -errno;
+		printk(UM_KERN_ERR "Failed to continue new process, pid = %d, "
+		       "errno = %d\n", pid, errno);
+		return err;
+	}
+
+	wait_stub_done(pid);
+
+	pid = data->err;
+	if (pid < 0) {
+		printk(UM_KERN_ERR "copy_context_skas0 - stub-parent reports "
+		       "error %d\n", -pid);
+		return pid;
+	}
+
+	/*
+	 * Wait, until child has finished too: read child's result from
+	 * child's stack and check it.
+	 */
+	wait_stub_done(pid);
+	if (child_data->err != STUB_DATA) {
+		printk(UM_KERN_ERR "copy_context_skas0 - stub-child reports "
+		       "error %ld\n", child_data->err);
+		err = child_data->err;
+		goto out_kill;
+	}
+
+	if (ptrace(PTRACE_OLDSETOPTIONS, pid, NULL,
+		   (void *)PTRACE_O_TRACESYSGOOD) < 0) {
+		err = -errno;
+		printk(UM_KERN_ERR "copy_context_skas0 : PTRACE_OLDSETOPTIONS "
+		       "failed, errno = %d\n", errno);
+		goto out_kill;
+	}
+
+	return pid;
+
+ out_kill:
+	os_kill_ptraced_process(pid, 1);
+	return err;
+}
+
+void new_thread(void *stack, jmp_buf *buf, void (*handler)(void))
+{
+	(*buf)[0].JB_IP = (unsigned long) handler;
+	(*buf)[0].JB_SP = (unsigned long) stack + UM_THREAD_SIZE -
+		sizeof(void *);
+}
+
+#define INIT_JMP_NEW_THREAD 0
+#define INIT_JMP_CALLBACK 1
+#define INIT_JMP_HALT 2
+#define INIT_JMP_REBOOT 3
+
+void switch_threads(jmp_buf *me, jmp_buf *you)
+{
+	if (UML_SETJMP(me) == 0)
+		UML_LONGJMP(you, 1);
+}
+
+static jmp_buf initial_jmpbuf;
+
+/* XXX Make these percpu */
+static void (*cb_proc)(void *arg);
+static void *cb_arg;
+static jmp_buf *cb_back;
+
+int start_idle_thread(void *stack, jmp_buf *switch_buf)
+{
+	int n;
+
+	set_handler(SIGWINCH);
+
+	/*
+	 * Can't use UML_SETJMP or UML_LONGJMP here because they save
+	 * and restore signals, with the possible side-effect of
+	 * trying to handle any signals which came when they were
+	 * blocked, which can't be done on this stack.
+	 * Signals must be blocked when jumping back here and restored
+	 * after returning to the jumper.
+	 */
+	n = setjmp(initial_jmpbuf);
+	switch (n) {
+	case INIT_JMP_NEW_THREAD:
+		(*switch_buf)[0].JB_IP = (unsigned long) uml_finishsetup;
+		(*switch_buf)[0].JB_SP = (unsigned long) stack +
+			UM_THREAD_SIZE - sizeof(void *);
+		break;
+	case INIT_JMP_CALLBACK:
+		(*cb_proc)(cb_arg);
+		longjmp(*cb_back, 1);
+		break;
+	case INIT_JMP_HALT:
+		kmalloc_ok = 0;
+		return 0;
+	case INIT_JMP_REBOOT:
+		kmalloc_ok = 0;
+		return 1;
+	default:
+		printk(UM_KERN_ERR "Bad sigsetjmp return in "
+		       "start_idle_thread - %d\n", n);
+		fatal_sigsegv();
+	}
+	longjmp(*switch_buf, 1);
+
+	/* unreachable */
+	printk(UM_KERN_ERR "impossible long jump!");
+	fatal_sigsegv();
+	return 0;
+}
+
+void initial_thread_cb_skas(void (*proc)(void *), void *arg)
+{
+	jmp_buf here;
+
+	cb_proc = proc;
+	cb_arg = arg;
+	cb_back = &here;
+
+	block_signals_trace();
+	if (UML_SETJMP(&here) == 0)
+		UML_LONGJMP(&initial_jmpbuf, INIT_JMP_CALLBACK);
+	unblock_signals_trace();
+
+	cb_proc = NULL;
+	cb_arg = NULL;
+	cb_back = NULL;
+}
+
+void halt_skas(void)
+{
+	block_signals_trace();
+	UML_LONGJMP(&initial_jmpbuf, INIT_JMP_HALT);
+}
+
+static bool noreboot;
+
+static int __init noreboot_cmd_param(char *str, int *add)
+{
+	noreboot = true;
+	return 0;
+}
+
+__uml_setup("noreboot", noreboot_cmd_param,
+"noreboot\n"
+"    Rather than rebooting, exit always, akin to QEMU's -no-reboot option.\n"
+"    This is useful if you're using CONFIG_PANIC_TIMEOUT in order to catch\n"
+"    crashes in CI\n");
+
+void reboot_skas(void)
+{
+	block_signals_trace();
+	UML_LONGJMP(&initial_jmpbuf, noreboot ? INIT_JMP_HALT : INIT_JMP_REBOOT);
+}
+
+void __switch_mm(struct mm_id *mm_idp)
+{
+	userspace_pid[0] = mm_idp->u.pid;
+	kill_userspace_mm[0] = mm_idp->kill;
+}